1. Field of the invention
The present invention concerns a fire gate adapted to support the combustible mass in a furnace, in particular a furnace for incinerating waste. The present invention also concerns the individual elements which constitute the grate.
2. Description of the prior art
Known combustible mass supporting grates are generally of the type comprising a plurality of identical individual elements. These grates are generally inclined so that the combustible mass tipped onto one end progresses along the slope. To achieve this, and also to obtain good distribution of the combustible mass along the grate, it is generally necessary to agitate the mass.
This agitation is generally achieved by movement of the individual grate elements, which are displaced relative to one another. Sharp projections or some special arrangement (staircase fashion, for example) enables the elements to modify the surface of the grate by virtue of their respective movements. Agitation is achieved in this way.
A grate of this kind is described in particular in document No. FR-A-1567605 (J. Martin).
In other implementations the elements are adapted to feed air into the combustible mass. Reference may be had in particular to French patent No. 1 006 739 describing an air communication system created between adjacent elements on relative longitudinal displacement thereof.
The main problem in incinerating products such as waste stems from the release of sulfides which tend to create deposits because their melting point is lower than that of their oxidation product. They are also the main contributors to making the environment extremely corrosive, which tends to create problems with regard to the service life of the incineration installation as a whole. It is therefore important to promote the conversion of these sulfides (in particular CaS, Na2S, FeS) into the corresponding solid oxides or sulfates and to adjust the combustion conditions accordingly to provide as regular and as complete combustion as possible.
The support grate elements are thus generally provided with orifices enabling the primary air blown in beneath the grate to supply oxygen for combustion.
Grate elements of this kind are known from document No. DE-U-6 905 562 (C. PETERS AG).
However, grates formed of elements with very many holes passing through them do not provide for correct control of the quantity of primary air introduced.
This is important since excess primary air is no more favorable to good combustion than any deficiency thereof.
The problem which arises is the clogging of the air feed orifices by the sulfide deposits themselves, or by as yet unburned elements of the combustible mass. This modifies the oxygen feed in a random manner, which affects the combustion.
A second problem which arises is that created by the raising of the mobile elements, which may be due to the accidental inclusion between two elements of some waste. The raising of an element has two effects: it changes the oxygen input, and it enables an element to penetrate under the grate, possibly into the primary air feed means. Increasing the weight of each element would enable this disadvantage to be obviated, but other problems would then arise, of construction in particular.
Another problem which arises is that of abnormal heating of the elements: in the event of blocking of the orifices enabling air to pass through an element, the element heats up abnormally, with all the implicit consequences: rapid deterioration and/or excessive thermal expansion resulting in binding against the adjacent elements.
A further difficulty results from the excessive quantity of flying ash which may be produced, causing rapid soiling of the parts of the incineration installation situated above the hearth.
The object of the present invention is to propose a new fire grate able to alleviate these disadvantages.